collections - Printing HashMap In Java

Question

I have a HashMap:

private HashMap<TypeKey, TypeValue> example = new HashMap<TypeKey, TypeValue>();

Now I would like to run through all the values and print them.

I wrote this:

for (TypeValue name : this.example.keySet()) {
    System.out.println(name);
}

It doesn't seem to work.

What is the problem?

EDIT: Another question: Is this collection zero based? I mean if it has 1 key and value will the size be 0 or 1?

Answer 1

keySet() only returns a set of keys from your hash map, you should iterate this key set and the get the value from the hash map using these keys.

In your example, the type of the hash map's key is TypeKey, but you specified TypeValue in your generic for-loop, so it cannot be compiled. You should change it to:

for (TypeKey name: example.keySet()) {
    String key = name.toString();
    String value = example.get(name).toString();
    System.out.println(key + " " + value);
}

Update for Java8:

example.entrySet().forEach(entry -> {
    System.out.println(entry.getKey() + " " + entry.getValue());
});

---

If you don't require to print key value and just need the hash map value, you can use others' suggestions.

Another question: Is this collection is zero base? I mean if it has 1 key and value will it size be 0 or 1?

The collection returned from keySet() is a Set. You cannot get the value from a set using an index, so it is not a question of whether it is zero-based or one-based. If your hash map has one key, the keySet() returned will have one entry inside, and its size will be 1.